Optical fiber alignment apparatus for a mechanical optical switch

ABSTRACT

An alignment apparatus for determining angular coordinates for offset and intersecting optical fibers in a mechanical optical switch has an analytical apparatus for imaging the end faces of the ferrules containing the opposing optical fibers of the switch for determining the respective axes of rotation of the mounting members, the locations of the optical fibers in the respective mounting members and coordinates of the optical fibers relative to the axis of rotation of the respective mounting members, the location of at least one reference point within one of the mounting members, and the relative angular coordinates of intersecting points between each of the closed curves of the plurality of optical fibers within the second mounting member and the closed curve of the first optical fiber as a function of the offset of the first and second mounting members and the reference point. The relative angular coordinates are passed to a measurement alignment apparatus for determining the angular coordinates of the intersecting points between each of the plurality of optical fibers and the first optical fiber as a function of optimally aligning the first optical fiber with each of the plurality of optical fibers.

This is a continuation-in-part application of application Ser. No.08/223,298, filed Apr. 5, 1994 now U.S. Pat. No. 5,438,638.

BACKGROUND OF THE INVENTION

The present invention relates generally to optical switches and morespecifically to an alignment apparatus for determining angularcoordinates of intersecting points of offset closed curves in amechanical optical switch rotatably coupling an optical fiber of a firstoptical fiber array with a second optical fiber of an opposing opticalfiber array.

There are generally two types of optical switches in use today:electronic optical switches and mechanical optical switches. Electronicoptical switches may be characterized as having no moving pans andperform the switching function, for example, by acousto-optically orelectro-optically diverting the light passing through the switch.

Mechanical optical switches, on the other hand, physically move opticalfiber elements to produce the switching function. Generally the physicalmovement of the optical fibers in mechanical optical switches is eithertransversal or rotational. One family of mechanical optical switchesuses focusing elements, such as lenses or the like, to focus the lightfrom one fiber to another. The use of such elements increases thetranslational tolerances of the switch but substantially decreases itsangular tolerances and increases its cost. The other family ofmechanical optical switches directly couple the light from one opticalfiber to the other. The optical fibers are positioned in opposingrelationship with the end faces of the optical fibers in substantiallyabutting relationship with each other. While this design eliminates thefocusing elements and increases the angular tolerances, it substantiallydecreases the translational tolerance of the switch.

U.S. Pat. No. 4,401,365 describes a rotary-type optical switch in whicha pair of opposing optical transmission path mounting members aredisposed on the same rotational axis. One mounting member may be fixedlysecured in a casing while the other member rotates on a central shaft.Alternately, the shaft may be fixed with one of the mounting membersrotating about the shaft. The shaft or the mounting member is directlyconnected to a motor so that one mounting member is rotatable withrespect to the other as the shaft or mounting member is rotated by themotor. The mounting members have respective plane surfaces which areclosely opposite each other. Optical fibers are secured in each mountingmember such that the end faces of the optical fibers in each mountingmember are concentric about the rotational axis of the mounting memberand lie on respective phantom circles having the same radii.

U.S. Pat. No. 5,037,176 describes another rotary-type optical switchthat includes first and second identical arrays of optical fibers heldin axial alignment and relatively rotatable about an axis of rotation toeffect optical coupling and decoupling of fibers in the opposing arrays.The optical switch has cylindrical switch bodies that receive the firstand second identical arrays of optical fibers. The switch bodies aremaintained in coaxial alignment by means of a split sleeve coupler. Atube surrounds the sleeve containing the fiber arrays and O-rings may bedisposed between the sleeve and the tube to permit an index matchingfluid to be retained within the switch to prevent back reflections. Theoptical switch described in the 176 patent is incorporated into anoptical switch assembly described in U.S. Pat. No. 5,031,994.

A critical factor in mechanical fiber optical switches (MFOS) is theprecise alignment of the opposing optical fibers in the switch.Currently, this requires the components of the switch to be made to veryprecise tolerances along with exacting manufacturing processes. As willbe described below, current MFOS fall short in cycle-to-cyclerepeatability, long-term repeatability and absolute alignment of theopposing optical fibers.

Mechanical fiber optic switches have unique bearing requirements thatare not found in other types of applications. These special requirementsneed to be examined to understand why current MFOS do not provide theoptimum alignment between switching fibers. The alignment tolerances forlight coupling between single-mode optical fibers is well known and neednot be discussed in detail here. Assuming no longitudinal or tiltmisalignment and the input and output fibers are identical, thefractional coupling transmission for optical fibers with lateralmisalignment is ##EQU1## where x is the lateral offset and w is the 1/e²radius of the irradiance pattern of the fundamental mode of the opticalfiber. The derivative of equation [1 ] is taken to obtain the change inloss for a given change in coupling efficiency. ##EQU2## Equation [2]can be rearranged to solve for Δx as a function of the lateral offset,radius of the fundamental fiber mode, and the change in loss. The resultis ##EQU3##

Using the above equations and assuming a transmission efficiency of theswitch must be repeatable within 0.01 dB on a cycle-to-cycle basis witha nominal transmission loss of less than 0.50 dB, maximum alignmenttolerance values can be calculated for cycle-to-cycle repeatability,long-term repeatability, and absolute alignment. Since the 1/e² radiusof the fundamental mode in standard single-mode fiber is roughly 5.0microns, the nominal loss of 0.50 dB corresponds to a lateralmisalignment of approximately 1.7 microns (according to equation [1]).According to equation [3], if the transmission changes less than 0.01 dBon a cycle-to-cycle basis, the misalignment of 1.7 microns must berepeated to within 0.015 microns, or 15 nanometers. The numericaltolerance are calculated for an optical fiber having a mode fielddiameter of 5.0 microns. Other optical fiber may, for example, have modefiled diameters, such as 5.1 or 5.6 microns. Different mode fielddiameters will change the numerical tolerances slightly but notsubstantially.

The 0.015 micron requirement is for cycle-to-cycle repeatability only.There is also a long term repeatability requirement where thetransmission efficiency must not change by more than 0.10 dB over about100,000 cycles. Applying the same analysis using equations [1] and [3],the position accuracy of the opposing fibers in the switch must repeatto within 0.15 microns on a long-term basis or about 1/4th of awavelength of visible light.

Referring now to FIG. 1A, there is shown an end view of a cylindricalshaft 10 inside a split sleeve 12. In an ideal world, the shaft 10 isperfectly round and has exactly the same outside diameter as the equallyperfectly round inside diameter of the split sleeve 12 with the shaft 10touching the split sleeve 12 along its entire circumference. A bore 14formed in the shaft 10 for holding the optical fibers is perfectly roundand concentric with the shaft 10 and split sleeve 12. FIGS. 1B and 1Cillustrate on an exaggerated scale the type of shaft 10, split sleeve12, and bore 14 that can be expected in the real, imperfect world. Noneof the elements 10, 12, or 14 will be perfectly round. Instead, shaft 10and split sleeve 12 will approximate a cylindrical surface, with localregions where the radius is slightly too large, or too small. This isshown in the figures as an ellipse. As can be seen from the figures, thepoints of contact between the split sleeve 12 and the shaft 10 willchange as one or the other rotates, or if any slight lateral torque, asshown by dashed ellipse 16, is applied to the shaft 10, so that fibers(not shown) in the shaft will not trace out concentric circles. Noticealso that, at the point of contact, the surface of the split sleeve 12is parallel to the surface of the shaft 10. The only force preventingthe shaft 10 from slipping in the split sleeve 12 is the frictionalforce between the two surfaces. The frictional force is incapable ofreliably providing the kind of cycle-to-cycle or long-term repeatabilitythat is needed. Furthermore, there is the paradox of lubrication. Inorder to extend the life of the bearing surfaces it is desirable tolubricate them, but lubrication reduces the frictional forces betweenthe two surfaces, resulting in more wobble.

FIGS. 1B and 1C illustrate an additional problem. The fibers alignthemselves to the shaft 10 via the bore 14 drilled along the axis of theshaft 10, and this bore 14 has its own set of tolerances. Specifically,the bore 14 will be slightly out of concentricity with the outsidesurface of the shaft 10, and like the outside surface of the shaft 10,it will be slightly out-of-round.

There are multiple dimensional tolerances that must be tightly specifiedif the input and output fibers of the switch are to rotate on identicalcircles that are precisely concentric. The design parameters that mustbe firmly controlled are:

Roundness of the input shaft outside diameter.

Roundness of the output shaft outside diameter.

Roundness of the input shaft inside diameter.

Roundness of the output shaft inside diameter.

Concentricity of the input shaft inside and outside diameters.

Concentricity of the output shaft inside and outside diameters.

Outside diameter of the input shaft.

Inside diameter of the input shaft.

Outside diameter of the output shaft.

Inside diameter of the output shaft.

Inside diameter of the split sleeve.

Roundness of the split sleeve inside diameter.

Diameters of the input and output fibers.

Concentricity of the input and output fibers.

To maintain an insertion loss of less than 0.50 dB, all of thesetolerances must add up to less than about 0.17 microns of misalignment.This is an extremely difficult task, and to accomplish it the individualcomponents (input fibers, output fibers, input shaft, output shaft, andsplit sleeve) must have several dimensional tolerances that aresub-micron. This is certainly not conducive for minimizing the costs ofindividual components, and is daunting in terms of manufacturability.

Another issue in mechanical fiber optic switch design is switchrepeatability. Referring to FIG. 2, there is shown a side view of theshaft 10 and sleeve 12 of FIGS. 1B and 1C with the sleeve 12 beingsectioned. The split sleeve 12 works with shaft 10 that is slightlylarger than the inside diameter of the unexpanded sleeve 12. Because thesleeve 12 is split, it can expand slightly to allow the shaft 10 (aferrule containing the optical fibers) to fit inside with no diametricalclearance. Diametrical clearance is unsatisfactory because it results inslop within the bearing, and there is needed less than 0.015 microns ofmisalignment non-repeatability between the opposing fibers to meet thecycle-to-cycle repeatability specifications.

As has been discussed with FIGS. 1B and 1C, the out of roundness on thepart of the shaft 10 and the sleeve 12 will cause the fiber to move oncurves that are not circles. However, barring wear in the bearing,out-of-roundness should not result in slop or lack of repeatability.Out-of-roundness will affect the total coupling efficiency, but not therepeatability. FIG. 2 shows the shaft 10 having an interference fit withthe sleeve 12. However, a second shaft 18 will most likely have aslightly different diameter owing to the inevitable tolerances inmanufacturing. If the second shaft 18 has a larger diameter than thefirst shaft 10, then it will expand the split sleeve 12 a little bit,resulting in an interference fit for the second shaft 18 but not thefirst shaft 10. Now the first shaft 10 can slop in the split sleeve 12.If the second shaft 18 has a smaller diameter than the first, then itwill wobble. No matter what happens one of the two shafts 10 or 18 willwobble within the split sleeve 12. To meet the cycle-to-cyclerepeatability requirement this wobble must be less that 0.015 microns,so the diameter of the two shafts 10 and 18 must be equal to about 0.008microns. This specification would require extremely expensive parts.However, for all practical purposes, meeting such a specification wouldbe impossible to do.

What is needed is an inexpensive mechanical fiber optic switch thatmeets the cycle-to-cycle repeatability, long-term repeatability, andabsolute misalignment specifications. Such a switch should use looselytoleranced commercially available off-the-shelf components and be easyto assemble without requiring fine alignment of the switch componentsand fibers. In addition, the switch should have a fiber mounting systemthat has minimum bearing wear and is insensitive to dimensionaldifferences of the components. Further, the switch should have goodstability over temperature.

SUMMARY OF THE INVENTION

Accordingly, the present invention is to an alignment apparatus fordetermining angular coordinates of intersecting points of offset closedcurves in a mechanical optical switch. The optical switch includes atleast a first optical fiber disposed within a first mounting memberrotating about a first independent and offset rotational axis with thefirst optical fiber positioned within the mounting member to move on afirst closed curve. A plurality of optical fibers are disposed within asecond mounting member with the plurality of optical fibers within thesecond mounting member rotating about a second independent and offsetrotational axis with the plurality of optical fibers positioned withinthe second mounting member to move on closed curves. The first andsecond mounting members have end faces in opposing relationship formingan optical interface between the first optical fiber and the pluralityof optical fibers. The first and second rotational axes are laterallyoffset from each other for offsetting the first closed curve from theclosed curves of the plurality of optical fibers for the establishingintersecting points between the closed curves of the plurality ofoptical fibers within the second mounting member and the closed curve ofthe first optical fiber. The alignment apparatus includes an analyticalapparatus for imaging the respective end faces of the first and secondmounting members for determining the respective axes of rotation of themounting members, the locations of the optical fibers in the respectivemounting members and their locations relative to the axis of rotation ofthe respective mounting members, and at least one reference point withinone of the mounting members. The relative angular coordinates ofintersecting points between each of the closed curves of the pluralityof optical fibers within the second mounting member and the closed curveof the first optical fiber are determined as a function of the offset ofthe first and second mounting members and the reference point. Ameasurement alignment apparatus receives the relative angularcoordinates of the intersecting points between each of the closed curvesof the plurality of optical fibers within the second mounting member andthe closed curve of the first optical fiber from the analyticalapparatus for determining the angular coordinates of the intersectingpoints between each of the plurality of optical fibers and the firstoptical fiber as a function of optimally aligning the first opticalfiber with each of the plurality of optical fibers.

In a further aspect of the invention the analytical apparatus includes amicroscope on which is mounted a holder assembly for receiving the firstand second mounting members and a light source for coupling light intothe first optical fiber and the plurality of optical fibers. A camera iscoupled to the microscope for generating images of the end faces of thefirst and second mounting members containing the first optical fiber andthe plurality of optical fibers. A video monitor is coupled to thecamera for generating a visual presentation of the end faces of themounting members. A frame grabber acquires images of the end faces ofthe mounting members for generating digital values representative of theacquired images. A computer receives, stores and processes the digitalimages under program control for determining the respective axes ofrotation of the mounting members, the locations of the optical fibers inthe acquired images and their location relative to the axis of rotationof the respective mounting members. The relative angular coordinates ofthe intersecting points between each of the closed curves of theplurality of optical fibers within the second mounting member and theclosed curve of the first optical fiber are determined as a function ofthe offset of the first and second mounting members and the referencepoint.

In still a further aspect of the invention the measurement alignmentapparatus includes a laser light source coupled to the first opticalfiber and first and second optical power meters coupled to the pluralityof optical fibers. The first optical power meter is coupled to amultimode reference fiber acting as the reference point in the secondmounting member and the second optical power meter is coupled to theremaining plurality of optical fibers. A computing means is coupled tothe first and second optical power meters and to the optical switch fordetermining under program control the angular coordinates of theintersecting points between each of the plurality of optical fibers andthe first optical fiber as a function of optimally aligning the firstoptical fiber with each of the plurality of optical fibers.

The objects, advantages and novel features of the present invention areapparent from the following detailed description when read inconjunction with appended claims and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A-1C are respective idealized and real world representations of aprior art coaxial alignment scheme for a mechanical fiber optic switch.

FIG. 2 is a side view of the prior art coaxial alignment scheme for amechanical fiber optic switch.

FIG. 3 is an exploded perspective view of the mechanical optical switchaccording to the present invention.

FIG. 4 is a perspective view of the ferrule drive assembly in themechanical optical switch according to the present invention.

FIG. 5 is an exploded perspective view of the ferrule drive assembly inthe mechanical optical switch according to the present invention.

FIG. 6 is a diagrammatic representation of the offset ferrules in themechanical optical switch according to the present invention.

FIGS. 7A and 7B are end views of the kinematically correct holderassemblies in the mechanical optical switch according to the presentinvention.

FIG. 8 is a simplified perspective of the offset input and outputferrules in the mechanical optical switch according to the presentinvention.

FIG. 9 is a representative alignment fixture for aligning the opticalfibers of the input port with the optical fibers of the output port inthe mechanical optical switch according to the present invention.

FIGS. 10A and 10B are a typical flow chart of a procedure for aligningthe optical fibers of the input port with the optical fibers of theoutput port in the mechanical optical switch according to the presentinvention.

FIG. 11 is a graph representing a mathematical model for couplingbetween two misaligned optical fibers used in the alignment procedurefor the optical ports in the mechanical optical switch according to thepresent invention.

FIG. 12 is a representation of an analytical station of an alignmentapparatus used for calibrating the mechanical optical switch accordingto the present invention.

FIG. 13 is a representation of a mechanical alignment station of analignment apparatus used for calibrating the mechanical optical switchaccording to the present invention.

FIG. 14 is a flow chart of a procedure for determining the angularcoordinates of intersecting points of opposing optical fibers of theinput port and output port in the mechanical optical switch according tothe present invention.

FIG. 15 is a representation of an inverted image of optical fibers inthe output ferrule in the mechanical optical switch according to thepresent invention.

FIG. 16 is a representation of the alignment condition for an arbitraryinput fiber in the mechanical optical switch according to the presentinvention.

FIG. 17 is a flow chart of a blind search routine for locating areference fiber in the mechanical optical switch according to thepresent invention.

FIG. 18 is a flow chart for a peaking routine for optimizing thealignment of opposing fibers of the input port and output port and forreturning the angular coordinates in the mechanical optical switchaccording to the present invention.

FIG. 19 is a perspective view of an improved mechanical optical switchaccording to the present invention.

FIG. 20 is a plan view of the mounting member drive line assembly of theimproved mechanical optical switch according to the present invention.

FIG. 21 is a cross-section view along line A-A' of the mounting memberof the improved mechanical optical switch according to the presentinvention.

FIG. 22 is a simplified representation of a remote fiber test systemusing the mechanical optical switch according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 3, there is shown an exploded perspective view of themechanical optical switch 20 according to the present invention. One usefor switch 20 is in remote fiber test systems. In such a system, theswitch 20 connects a remote test unit, such as an optical time domainreflectometer, optical power meter, or the like, to various opticalfibers in order to evaluate them. Another use is in conjunction withcentral office telephone switches for redirecting phone signals to adifferent optical fiber line when the original line is damaged.

Switch 20 has a housing 22 having a base 24, end walls 26 and 28, andsidewall 30 forming a partial cavity 32. Within the cavity 32 is acentral pedestal 34 and bearing supports 36 rising from the base 24. Thebearing supports 36 are disposed between the central pedestal 34 and theend walls 26 and 28. A removable sidewall 38 and top plate 40 areprovided for enclosing the housing cavity 32. Mounted on top of thehousing 22 is a circuit board 42 containing the electronic circuitry forthe switch 20. The electronic circuitry contains a storage device ordevices for holding angular coordinates related to intersecting pointson closed curves between two opposing optical fibers. It also containlogic circuitry for validating requests to and functions of the switchand for generating interrupt commands for stopping switch functions anduser error codes. Secured to the outside of the housing 22 adjacent tothe end walls 26 and 28 are stepper motor brackets 44. Secured to eachbracket 44 is a stepper motor 46. Extending from each stepper motor 46is a shaft on which is secured a toothed spur gear 48. Mounted on theoutside of each end wall 26 and 28 is a photodetector bracket 50.Mounted on each bracket is a photodetector 52 having a light emittingelement and a light sensitive element.

A bore 54 is formed in each of the end walls 26 and 28. Bearings 56 arepress fit into each bore 54 from the cavity 32 side of the end walls 26and 28. Bearings 58 are also press fit into the bearing supports 36.Flange shaft seals (not visible in this figure) are mounted within eachbore 54 from the outside of the cavity 32 and held in place by sealplates 60 mounted on the outside of the end walls 26 and 28. Extendingthrough the seal plates 60, the flange shaft seals, and bearings 56 and58 are rotatable drive shafts 62 having a central bore 64 for receivinginput and output optical fibers 66 and 67. Mounted on each drive shaft62 are slotted wheels 68 having a slit 70 formed therein. A portion ofeach slotted wheel 68 is positioned within a gap between the lightemitting element and the light sensitive element of the photodetector52. Also mounted to the rotatable drive shafts 62 are drive shaft spurgears 72 which engages the respective toothed spur gears 48 of thestepper motor 46. Secured to one end of each of the drive shafts 62 areflexible drive shaft couplings 74. Within the other end of the flexiblecouplings 74 are mounting members (not visible in this drawing) thathold the optical fibers 66 and 67 of the switch 20. Spring clamps 76 aremounted on the central pedestal 34 for hold the mounting members withinoffset V-grooves formed in the pedestal 34. The spring clamps 76 and theoffset V-grooves form the holder assemblies for the mounting members,which will be described in greater detail below. The enclosed cavity 32may be filled with an appropriate index matching fluid to reduce backreflections of the input light passing between the input fiber andoutput fiber. The index matching fluid also acts as a lubricant for theV-grooves and the bearings 58.

The housing 22, removable sidewall 38, and top plate 40 may be made ofsuch materials as milled aluminum, stainless steel, or molded plastic.In the current design, these parts are milled aluminum. The rotatingmeans in the form of the stepper motor 46 needs to achieve 0.14 degreesof rotational accuracy, be inexpensive, use relative little power and besmall. An example of such a stepper motor 46 is manufactured and sold byHSI, Inc., Waterbury, Conn. under part number HSA33700. This particularstepper motor has an angular control specification to 0.09 degrees.Since the backlash is large for this particular motor a home positionindicator is provided with the photodetector 52 and the slotted wheel68. The photodetector 52 may be any commonly available device, such asthe Sharp GP1L01F manufactured and sold by Sharp Corp., Camus, Wash.that generates an electrical signal when light passes from the lightemitting element to the light receiving element. The slotted wheel 68may be made of any appropriate material having adequate rigidity andcapable of having a narrow slot formed in it. In the preferredembodiment, the slotted wheel 68 is formed from a 1 mil polycarbonatefilm having a 0.001 inch slot 70 formed therein. The film is laminatedonto an aluminum stiffening plate. As an alternative to the steppersmotors 46, DC motors having high resolution encoders may be used. Theferrule drive shaft 62 may be formed of any appropriate material that issubstantially rigid and resistant to wear. In the preferred embodiment,the rotatable drive shaft 62 is a stainless steel rod having an outsidediameter of one-forth of an inch. The central bore 64 has a diameter ofone-tenth of an inch.

Referring to FIG. 4, there is shown a perspective view of the mountingmember drive system for the mechanical optical switch 20. The drivesystem includes input and output sections 80 and 82 which areessentially the same with the exception of the positioning of theoptical fibers within the mounting member, which will be described ingreater detail below in relation to ferrules 86. The elements of theoutput section 82 are essentially the same as the input section 80. Theoutput section 82 has the rotatable drive shaft 62 on which is mountedthe slotted wheel 68 and the drive shaft spur gear 72. The drive shaft62 passes through seal plate 60, the flange shaft seal 94, and bearings56 and 58. Attached to one end of the drive shaft 62 is the flexibledrive shaft coupling 74. The flexible coupling 74 is provided to reducethe lateral torque being applied to the ferrules 86 during rotationalmovement, which would cause misalignment of the optical fibers in theswitch 20. An appropriate flexible coupling may be obtained fromServometer Corp., Ceder Grove, N.J. under part number FC-9. Secured tothe opposite end of the flexible coupling 74 is ferrule 86 contained ina ferrule assembly 88. Within each ferrule 86 are secured the opticalfibers 66 and 67 of the switch 20, which are in intimate opposingrelationship to each other. To maintain this relationship, clamp collars96 are mounted on the ferrule drive shafts 62 on either side of theinner bearings 58 to compress the flexible coupling 74 to keep the endfaces of the ferrules 86 in compression.

Referring to FIG. 5, there is shown an exploded perspective view of themounting member drive assembly. Elements in this figure are numbered thesame as like elements in the previous figures. The ferrule assembly 88consisting of a ferrule coupler 90 and the ferrule 86. In the preferredembodiment the ferrule coupler 90 is made of stainless steel but othersuitable materials may be used. Alternately, a ferrule strain relief 92may be secured within the ferrule coupler 90. A representative ferrulestrain relief 90 may be purchases from Stimpson Co., Inc., Bayport,N.Y., under part number A3215. The ferrule 86 is secured in the ferrulecoupler 90. The ferrule 86 is formed of a borosilicate industrial opticsglass. A representative type of ferrule is the HC type manufactured andsold by Nippon Electric Glass, Des Plaines, Ill. This particular type offerrule has an outside diameter tolerance of ±5 microns, an out ofroundness specification of ±1 micron, and inside diameter tolerance of±2 microns. As was previously described, using a ferrule with thesetolerances in prior art optical switches would not provide thecycle-to-cycle repeatability, long, term repeatability, and absolutealignment required for a workable mechanical optical switch. However,applicant's mechanical optical switch 20 overcomes the mechanicaltolerance problems of current mechanical optical switches by offsettingthe ferrules 86 so as to rotate about independent axes instead ofcoaxially aligning and rotating the ferrules about a single axis as inthe prior art.

Referring to FIG. 6, there is shown a representation of two opposingferrules 100 and 102, rotating on independent axes 104 and 106, witheach ferrule 100 and 102 containing an optical fiber 108 and 110 actingas an optical transmission path. In the preferred embodiment, theoptical fibers are single-mode fibers having a core diameter ofapproximately 10 microns and an outside diameter of 125 microns. Otheroptical transmission paths may also be used, such as multimode opticalfibers without departing from the scope of the invention. The opposingoptical fibers 108 and 110 are positioned to move along closed curves112 and 114 as the ferrules 100 and 102 are rotated. The close curves112 and 114 intersect at points 116 and 118 on the respective curves.Assuming the curves 112 and 114 remain closed throughout the 360 degreesof rotation of the ferrules 100 and 102, the intersection points 116 and118 will be stable and will accurately represent the optimum alignmentposition for the two opposing fibers 108 and 110.

Referring to FIGS. 7A and 7B, there are shown end views of one of thetwo offset holder assemblies 120 formed or mounted on the pedestal 34 ofthe mechanical optical switch 20. Each holder assembly 120 has aV-groove structure 122 having an apex 124 and angularly extendingsidewalls 126 and 128 forming a V-shaped cavity 130. Bonded to thesidewalls 126 and 128 are thin strips of wear resistant material 132 and134, such as glass, ceramic, or the like. Configuring the holderassembly 120 in this manner allows the V-groove structure 122 to beformed from inexpensive materials, such as aluminum, plastic, or thelike, while at the same time providing an extremely durable bearing. Amore expensive, but possible design could use V-grooves made directlyfrom the wear resistant material.

Ferrules 86, shown considerably out-of-round for illustrative purposesonly, are respectively received in each of the V-groove cavities 130formed on the pedestal 34. Spring clamps 76 are positioned over thecavities 130 to secure the ferrules 86 in the V-groove structures 122.The sidewalls 126 and 128 of each V-groove structure 122 provide twocontact points for the ferrule 86 while the spring clamp 76 provides thethird. This three-point mount is kinematically correct. A kinematicmount used in this specification means a mount with all forces resolvedthrough a concurrent point. The retaining surfaces, the sidewalls 126and 128 and the spring clamp 76, are tangent to the surface of theferrule 86, resulting in a minimum energy configuration that is verystable, even when the ferrule 86 is not perfectly round. This comparesto the prior art switches where the number of contact points is unknown,and varies from switch to switch, even during rotation. The spring clamp76 in each holder assembly 120 is easily capable of small motion, so itcan accommodate thermal expansion of the ferrule 86 or anyout-of-roundness without slop (random movement) of the ferrule itself.Even if the ferrule 86 is considerably out-of-round the fibers insidethe ferrule will still trace out closed curves. This eliminates anywobble caused by the dimensional variations between ferrules, asexhibited in prior art mechanical optical switches. It should be notedthat the practice of this invention is not limited strictly to theV-groove structure and clamp configuration and other kinematicallycorrect holder assemblies may be used without departing from the scopeof the invention.

Beating wear is a critical problem for any mechanical optical switch 20.The bearing wear on the V-groove structure 122 occurs only along ainfinitesimally thin line on each sidewall 126 and 128 surface. However,wear on the ferrule 86 occurs along its entire surface. Assuming thethickness of the material removed through wear is inversely proportionalto the surface area of the bearing, the wear rates on the V-groovestructure 122 should be hundreds or thousands of times greater thanthose of the ferrule 86. Bonding the wear resistant strips 132 and 134to the sidewalls 126 and 128 reduces the wear on the V-groove structure122. Additionally, control of the switch can be designed so, on theaverage, both ferrules 86 rotate the same number of degrees during any100,000 cycles. This would in theory result in even wear rates for bothV-groove bearings so that the ferrules 86 settle into the respectiveV-groove structures 122 by the same amount, thus preserving theirrelative alignment.

Referring to FIG. 8, there is shown a perspective view of the offsetV-groove holder assemblies 120 formed on the pedestal 34 of themechanical optical switch 20. Mounted in the V-grooves 140 and 142 areinput and output ferrules 144 and 146 containing input and outputoptical fiber arrays 148 and 150. Each fiber array 148 and 150 may beformed of a single optical fiber 152 or multiple optical fibers. Theouter walls of the ferrules 144 and 146 and the spring clamps 76 are notshown for clarity. The wear resistant strips 132 and 134 are shown inthe currently preferred configuration where the separate wear resistantstrips are bonded to the opposing ends of the sidewalls 126 and 128 ofthe V-grooves 140 forming a double ended bearing for the ferrules 144and 146. The spring clamps 76, as shown in FIG. 3, are slotted to formfirst and second spring clamp members positioned over each set of wearresistant strips for securing the ferrules 144 and 146 in the V-groovecavity 130. Alternately, the wear resistant strips 132 and 134 may beconfigured to line the complete sides of the V-grooves 140. As is shownin the figure, the input ferrule 144 is slightly offset from the outputferrule 146. Because each ferrule 144 and 146 is highly constrained inits kinematically correct holder assembly 120, each fiber 152 of theinput fiber array 148 traces out a closed curve when the input ferrule144 rotates. These closed curves are approximately circles, but theactual shapes of the curves are not important. The curves could beellipses, or any similar shaped closed curve. The same thing applies tothe optical fibers 152 in the output fiber array 150. As was describedwith reference to FIG. 6, the closed curves of the optical fibers 152 inthe input and output fiber arrays 148 and 150 are not concentric. Thatis any optical fiber 152 positioned to move on a closed curve in theinput fiber array 148 will not be mirrored by any optical fiber 152positioned to move on a closed curve in the output fiber array 150. TheV-grooves 140 and 142 are deliberately offset in order to throw anyinput optical fiber closed curve out of concentricity with any outputoptical fiber closed curve.

Because the closed curves of the respective input and output opticalfiber arrays 148 and 150 are not concentric, they intersect at exactlytwo points. It is because of this fact that perfect alignment isachieved between the optical fibers 152 of the input optical fiber array148 and the optical fibers 152 of the output optical fiber array 150.Because there is no wobble or slop in the ferrule bearings, thekinematically correct holder assemblies 120, the curves are reallyclosed, and because they are closed the angular coordinates of theintersection points are stable. This means that, for some angularcoordinates of the input and output ferrules 144 and 146, an opticalfiber 152 of the input fiber array 148 comes into perfect alignment withan optical fiber 152 of the output fiber array 150 at the intersectionpoints. And, because the curves close, the angular coordinates arestable. They repeat over and over with extreme precision. Dynamically,if the trajectory of the system in phase space closes, then it isstable, periodic, and predictable. If the trajectory does not close,however, then the system can be chaotic.

Another important advantage is achieved by offsetting the input andoutput ferrules to rotate about independent and separate rotationalaxes. Each ferrules 144 and 146 may be loaded with any number of fibers152. Some of the fibers 152 will be located about the edge of the insidediameter of the ferrules 144 and 146, and some will be located towardthe center. By offsetting the ferrules 144 and 146, the closed curvesscribed by the input fibers along the edge of the ferrule 144 can bemade to intersect all of the output fibers of ferrule 146, even thosethat are located more toward the center. To do this, the offset betweenthe two ferrules 144 and 146 should nominally be such that the closedcurve traced out by the input fiber intersect the center of the outputferrule to within a tolerance of 1/2 the fiber diameter. In prior artdesigns, output fibers that are located near the center cannot beconnected to input fiber that are on the edge. This means that an N X Nswitch can be built with more of its fibers concentrated toward thecenter than would be possible with prior art mechanical opticalswitches. This is an important advantage and objective of the inventionbecause the angular tolerance required to achieve a given alignmentdecreases as the fibers move further from the center of the ferrule. So,when the fibers are far from the center of the ferrule, it requires moreaccurate angular resolution of the apparatus that rotates the ferrules.This would require, for example, the use of more expensive steppermotors 46 in the prior art designs whereas, in the present invention,less precise and therefore, less expensive stepper motors 46 can beused.

Another advantage and objective of the present invention is that theoptical fibers 152 in the input and output optical fiber arrays 148 and150 may be randomly configured in the input and output ferrules 144 and146. That is, it is not necessary to arrange the fibers 152 in the array148 and 150 in neat little patterns. Each fiber can follow its ownclosed curve. It make no difference to the operation of the switch, solong as the closed curves of all the input fibers 152 of the input fiberarray 148 intersect the closed curves of all of the output fibers 152 ofthe output fiber array 150. Compare this design to the prior art wheresomething is required to hold the fibers against the surface of theinside diameter of the ferrule or position the fibers on a concentriccircle. Furthermore, that something must be very accurately dimensionedor the fibers will not be held tightly, and this will affect theconcentricity, diameter, and roundness of the circles these fibersshould travel.

An objective of the present invention is to produce a mechanical opticalswitch 20 that is easy to manufacture. As has been previously described,the mechanical optical switch 20 does not require precise positioning ofthe individual fibers 152 of the input and output fiber arrays 148 and150 in the input and output ferrules 144 and 146 of the switch 20. Theswitch 20 of the present invention maybe configured as a 1×N switchhaving a single input port and multiple output ports or it may beconfigured as an N×N or N×M switch with multiple input ports andmultiple output ports. In any configuration, the positioning of theoptical fibers 152 is similar. In a 1×N switch, the input ferrule 144 isfilled with optical fibers 152. Epoxy is added to the ferrule 144 tofill the voids between the fibers 152. All but one of the optical fibers152 are then snipped at the end of the ferrule 144 leaving a singleoptical fiber 152 as the optical port. The same process is used for N×Nand N×M optical switches with the exception that less or no fibers 152are snipped. Likewise, the same process is used for producing the outputports for the switch 20. The important fact here is that no precisepositioning of the fibers 152 within the ferrules 144 and 146 isnecessary. This substantially reduces the manufacturing costs of theswitch 20.

Alternately, a plug device may be used in forming the optical ports ofthe switch 20. The plug is positioned in the ferrules 144 and 146 andthe fibers 152 are positioned between the plug and the inside wall ofthe ferrules. Epoxy is used to fill the ferrules 144 and 146. In eitherprocess, the ends of the ferrules 144 and 146 containing the fiber 152are then ground and polished.

The input and output ferrules are then mounted in the holder assemblies120 of the switch 20 and connected to the flexible couplings 74 of theferrule drive system with the input and output fibers 66 and 67 (FIG. 3)passing through the central bores 64 of the ferrule drive shafts 62. Itis worth noting that the assembly of the mechanical components of theswitch is independent of the location of the optical fibers 152 in theinput and output ferrules 144 and 146. As an example, the slotted wheels68 are mounted on the ferrule drive shafts 62 without regard to theposition of the fiber 152 within the ferrules 144 and 146. Thepositioning of the slots 70 in the wheels 68 to the photodetectors 52establishes the starting reference points for the fibers 152 in theirrespective ferrules 144 and 146. The sidewall 38 is secured to thehousing 22 and the cavity 32 is filled with an appropriate indexmatching fluid. The top plate 40 is secured to the housing and theswitch 20 is ready for the alignment process.

FIG. 9 shows an representative alignment fixture for determining theintersection points of the closed curves of the input optical fiberswith the closed curves of the output optical fibers. It should be notedthat any fiber 152 lying substantially on the axis of rotation of eitherof the ferrules 144 or 146 will not move on a closed curve but act as apoint. For this reason, any fiber 152 on the axis of rotation of eitherof the ferrules 144 and 146 will not be used as an optical port. Thealignment fixture has a controller 160, such as a computer, a lasersource 162, either 1310 nm or 1550 nm, a single-mode coupler 164, twooptical power meters 166 and 168, an electronic switch 170 and a bank ofphotodiodes 172. The computer 160 controls both the optical switch 20and the electronic switch 170, and records the analog signals from thepower meters 166 and 168. The computer locates the angular alignmentcoordinates of each port on the optical switch 20 by following aprocedure as exemplified by the flow chart of FIG. 10. The thresholdvalues in the procedure are not given since they may vary from fixtureto fixture based on the laser light source used, the type of photodiodesemployed and the type of power meters used.

The basic alignment procedure uses a mathematical model for couplingbetween two misaligned gaussian beams. This model is generally a goodapproximation for the optical transmission between misalignedsingle-mode fibers, since the fundamental modes of these fibers arenearly gaussian. The model assumes the two optical fibers are exactlyidentical, and that there is no longitudinal or angular misalignmentbetween them. These assumption are valid since the ferrules 144 and 146are ground and polished prior to installation in the switch 20 and clampcollars 96 are used to maintain the ferrules 144 and 146 in opposingcontact. The mathematical model has previously been set forth inequation 1 where T is the optical transmission, x is the lateral offsetbetween the two fibers and w is the 1/e² radius of the irradianceprofile of the fundamental mode. FIG. 11 illustrates this functionplotted against a logarithmic scale. The function has a single maxima,obtained when the two fibers are exactly coaxial. The procedure locatesthis maxima by moving the first fiber, and then the second, in such away as to maximize the optical transmission of the switch.

For the smooth curve shown in FIG. 11, the iterative procedure in FIG.10 steadily converges on the maxima, where the two fibers are in exactalignment. In the real world, however, the curve is lumpy below acertain level, so at low light levels the curve has local maxima thatcan fool the procedure. These local maxima are much lower, by 20 to 30dB, than the global maxima, so the procedure must not align to them, orthe switch's insertion loss will be to high. This is the reason theprocedure makes large steps (either clockwise or counter-clockwise) whenthe transmission is below some predetermined threshold, which may becalled Local Maxima Threshold, or LMT. These small local maxima aregenerally only a few degrees wide, so by searching with 5 or 10 degreesteps the procedure avoids them, finding its way above the LMT, usuallywithin 5 degrees of the global maxima.

Although a preliminary search with large steps greatly diminishes thedanger of inadvertently aligning the switch to the local maxima, theprocedure is not fool-proof. As an extra precaution, the procedurechecks the absolute transmitted power before deciding whether or not theport is properly aligned. If the absolute power is too low, but cannotbe improved by adjusting the two motors (using the smallest stepincrement) then either the switch has a defective component, or it isaligned to a local maxima. If this happens, the procedure employs aspecial problem solving subroutine, labeled 1 in flow chart of FIG. 10.

The problem solving subroutine will use information about how bad thetransmission efficiency is, in order to conduct another search usingincrements that are larger than the stepper motor's smallest step, butsmaller than 10 degrees. It is believed that the LMT can be adjusted sothat these types if problems will be very rare, in which case theprocedure may simply try to align another port, and leave the difficultones for an experienced human operator.

When aligning switches with many ports, it may be impractical to try toalign the ports sequentially. Instead, it may he simpler to examine eachof the output ports, seeing which is closest to the input port bymeasuring the optical power at each of the photodiodes, and align thatone first. After aligning the first port, the procedure could align thenext closest port. Generally, this procedure will align the output portsout of sequence, but it will be faster, and the procedure can alwaysre-number the ports after completing the alignment procedure.

The procedure starts with the controller 160 rotating the input andoutput ferrule drive shafts 62 to their home positions. Their homepositions are electrical signals from the photodiodes 52 when the slots70 of the slotted wheels 68 pass between the light emitting elements andthe light receiving elements of the photodiodes. The procedure sets theelectronic switch 170 to port 1, box 180, and rotates the input ferrule144 to maximize the optical signal at the port 1 photodiode 172. Theoutput ferrule 146 is then rotated to naximize the optical signal, box182. If the optical signal is greater than the thresholds, box 184, thenthe optical signal is maximized again by sequentially rotating steppermotors 46 for the input and output ferrules 144 and 146 using thesmallest step increments, boxes 186 and 188. These steps are repeateduntil the optical signal no longer increases, box 190. If the insertionloss is within specifications, box 192, then the port is aligned. Thenumber of degrees each stepper motor 46 has turned from their respectivehome positions are stored in a memory located on the circuit board 42mounted on the switch 20. The electronic switch 170 is set to the nextport and the ferrules 144 and 146 are set to the home position, box 194,where the process is repeated for the next port, box 180.

If the optical signal is less than the threshold after the first motorturning, box 184, then the procedure turns motor 1 in the range of 10degrees clockwise and maximizes the optical signal by turning motor 2,box 196. If the optical signal does not improve, motor 1 is turned inthe range of 20 degrees counter-clockwise and motor 2 is turned tomaximize the optical signal, box 200. If the optical signal improvesafter the approximately 10 degree clockwise rotation or the approximate20 degree counter-clockwise rotation of motor 1 and the maximizing ofthe optical signal by turning motor 2, boxes 198 and 202, then theroutine continues in the appropriate direction with maximizing theoptical signal with motor 2, boxes 204 and 206. If the optical signal isgreater than the threshold after this process, then the routine jumps tothat portion of the procedure where motor 1 and 2 are turned using thesmallest increment, boxes 186 and 188. If the optical signal is greaterthan the insertion loss, box 192, then the port is aligned, box 194,otherwise the routine jumps to the special problem solving routine, box186. If after the clockwise and counter-clockwise rotations of themotors, the optical signal is less than the threshold, box 210, then theroutine jumps to the special problem solving subroutine, box 186.

The procedure of FIG. 10 is designed to find one of the two intersectingpoints on the closed curves of the input and output optical fiberdefining optical ports. The procedure could easily be modified to findboth intersection points. This would be advantageous for fasterswitching between ports of the optical switch 20 in that the closestintersecting point of the designated ports could be more quicklyaccessed. Further, the procedure just described assumes a blind search,that is nothing is known about the locations of the fibers 152 withinthe ferrules 144 and 146. An improved apparatus for and method ofaligning fibers within ferrules 144 and 146 is shown in FIGS. 12 through18. The alignment fixturing consists of an analytical station 220, shownin FIG. 12 and a measurement alignment station 230, shown in FIG. 13.The analytical station 220 includes a light source 221, such as afrosted florescent light, and an optical microscope 222, such asmanufactured and sold by Buehler and used for examining the ferrules offiber-optic connectors. The microscope is used with a 5× objective inthe alignment implementation of the present invention. Depending on thenumber of fibers 152 in the input and output ferrules 144 and 146, theobjective may be larger or smaller. For example, a 10× or 20× objectivemay be used for a lower port count mechanical optical switch 20 whereasa 2× objective may be used for a high port count mechanical opticalswitch 20. A black and white CCD camera 223, such as Model No. KP-M1manufactured and sold by Hitachi Denshi, Ltd. is coupled to themicroscope 222. The output of the CCD camera 223 is coupled to a videomonitor 224, such as manufactured and sold by Hitachi Denshi under ModelNo. VM920/VM921. The video monitor 224 output is coupled to aframe-grabber 225, such as Computer EYES LPT, Model CAT-100. The outputof the frame grabber 225 is coupled to a computer 226 containing ComputeEYES frame grabber software. The measurement alignment station 230includes a solid state laser 23 1, such as a 1310 nm or 1550 nm laserused in telecommunications transmission equipment, power meters 232 and233, such the Model TFC200 Optical Power Meter manufactured and sold byTektronix, Inc., and a computer 234. The individual computers 226 and234 may be connected together via a network or may be a single computershared by both stations. Irrespective of the configuration of theindividual computers 226 and 234, the data output of the analyticalstation 220 is used by the measurement alignment station 230 foraligning the opposing fibers 152 within the ferrules 144 and 146.

The analytical station 220 acquires images of the respective end facesof the input and output ferrules 144 and 146 containing the opticalfiber arrays 148 and 150 for determining the centers of each fiber 152within the ferrules 144 and 146, the axes of rotation of the respectiveferrules 144 and 146 and the angular alignment coordinates of each fiber152 within the respective ferrules relative to a reference point withineach ferrule. The reference point for each ferrule is a fixed pointwithin the ferrule that is discernable in the acquired images. In thepreferred embodiment of the alignment procedure, the reference point isa multimode fiber, referred to hereinafter as the reference port. Amultimode fiber is chosen because it is substantially larger in diameterthan the single-mode fibers and is readily identifiable in the imagedend faces of the ferrules 144 and 146. This makes it much easier to findand singularly identify the reference port than if it where asingle-mode fiber. The need for consistent, even illumination across thefiber 152 cores for imaging affects the procedure for building theferrules 144 and 146. The same fiber array or bundle 235 is used forboth the input and output ferrules 144 and 146 with the ferrules locatedat opposite ends of the fiber bundle 235 as shown in FIG. 12. Thisallows easy illumination of the fiber 152 cores by simply pointing theopposite ferrule toward the diffuse light source 221. After scanning theferrules' images into the computer, the fiber bundle 235 is cut in themiddle to separate the two ferrule assemblies. The fiber bundle 235consists of a number of single mode fibers and the multimode referencefiber. In a 1×N optical switch, all but one single-mode fiber is cut atthe input ferrule 144. The measurement alignment station 230, operatingunder program control, selectively rotates the input and output ferrulesof the assembled switch to optimally align the fiber or fibers 152 ofthe input optical fiber array 148 with the fibers of the output opticalfiber array 150.

Referring to FIG. 14, there is shown a flow chart for aligning thefibers 152 of the input and output optical fiber arrays 148 and 150disposed in the input and output ferrules 144 and 146 and fordetermining the angular coordinates for each aligned input fiber with anoutput fiber. The first step 245 of the procedure is to place one of theferrules in a simple fixture, patterned after the V-groove structure ofthe switch, mounted on the microscope 222 stage. For explanationpurposes, the output ferrule 146 is described below.

The next step 246 is to acquire three images of the ferrule, with eachimage at approximately one hundred and twenty degrees rotated from itsposition in previous image. The images are digitized and stored in thecomputer 226 for analysis. For example, the output ferrule 146 is imagedin the three orientations with the input ferrule 144 illuminated by thelight source 221 and the microscope 222 light off. The acquired imagesare nearly binary, consisting of the illuminated cores of the fibers 152on a black background. Because of the binary nature of the images, thefiber cores are relatively easy to find and accurately located. Atypical location error is on the order of one-half of a pixel, or aboutone micron using a 5× objective in the microscope 222. FIG. 15 is aninverted image of the illuminated fibers 152 in the output ferrule 146.The small spots 262 are the illuminated cores of the single-mode fibersand the single large spot 262 is the illuminated core of the multimodereference port or fiber. A corresponding image of the input ferrule 144for a N×N mechanical optical switch 20 would look similar to the outputferrule 146 image. An image of the input ferrule 144 in a 1×N mechanicaloptical switch 20 would show a single small spot for the single inputfiber. Using rotated images of one of the fibers within the ferrulesfinds the true axis of rotation, even if the ferrule's inside andoutside radii are not concentric. The only requirement imposed on theinput and output ferrules' geometry is that the outside radius beapproximately round.

The next step two steps 247 and 248 locate the center of each fiber andthe coordinates of the ferrule's center of rotation. The alignmentprocedure locates the center of each ferrule by analyzing one of thestored images of the ferrule. The procedure compares each stored pixelto a threshold value. Any pixel value greater than the threshold is thencompared to its eight neighboring pixel values to determine if it isgreater than any of its eight neighboring pixels. If so, the averagecenter of illumination is determined the region around the pixel equalto the fiber core size. The average center of illumination for eachlocal maxima above the threshold value is stored as the coordinates ofthe fibers 152. The alignment procedure determines the true axis ofrotation of the output ferrule 146 by analyzing the ferrule at differentrotational orientations. The center of the multimode reference port 262in the output ferrule 146 is determined for each of the three images andthe center and radius of rotation is determined by solving the followingthree simultaneous equations:

    (x.sub.2 -a).sup.2+ (y.sub.2 -b).sup.2 =r.sup.2            [ 5]

    (x.sub.3 -a).sub.2+ (y.sub.3 -b).sup.2 =r.sup.2            [ 6]

    (x.sub.1 -a).sup.2+ (y.sub.1 -b).sup.2 =r.sup.2            [ 4]

In these equations (x₁,y₁), (x₂ y₂), and (x₃,y₃) are the coordinates ofthe fiber core in the three images, (a, b) is the coordinate of thecenter of rotation and r is the radius of rotation. The solutions are:##EQU4## The above equations locate the coordinates of the axis ofrotation for the ferrule 146 and the image analysis determines thelocations of each fiber 152 in the microscope's coordinate system forthe output fiber array 150. A coordinate transformation determines thelocation of each fiber 152 in the output ferrule 146 in a coordinatesystem located on the rotation axis of the ferrule. Suppose thatx_(l).sbsb.i and y_(l).sbsb.i are the coordinates of the i'th fiber in ageneral laboratory reference frame, while x_(f).sbsb.i and y_(f).sbsb.irepresent their locations in a coordinate system centered on theferrule's axis. Both coordinate systems are Cartesian, and their x and yaxes are parallel. The coordinate transformation equations are:

    x.sub.1.sbsb.i =x.sub.f.sbsb.i -a                          [10]

    y.sub.f.sbsb.i =y-b                                        [11]

where a and b represent the x and y coordinates of the center of theferrule in the microscope's laboratory reference frame.

The next step 249 places the input ferrule 144 in the microscope 22fixture. Three images of the end face of the input ferrules are acquiredat three different rotational orientations and the three simultaneousequations are solved for (a,b) and r. The coordinates of the ferrule'saxis of rotation is determined using either the multimode referencefiber 262 if the mechanical optical switch 20 is an N×N type switch orthe single-mode input fiber if the switch 20 is a 1×N type switch. Thetrack radius of the input fibers or fiber, or the distance from therotational axis of the input ferrule 144 to the input fiber's core, isdetermined.

The next step 250 is to calculate the radial coordinates of each fibercore 260 relative to the center of the ferrule 146 and to calculate therelative change in alignment coordinates for each fiber relative to thereference fiber 262. The offset distance of the V-grooves, which in turnis the offset distance of the ferrules, is approximately known from thespecifications of the switch or can be measured directly with amicrometer. In addition, a convention for positive and negative rotationof the ferrules is defined. Positive rotation is defined as acounter-clockwise rotation when looking at the optical interface ofeither ferrule. Negative rotation is defined as clockwise rotation. Thepositive x-axis and y-axis have their origins at the center of theoutput ferrule with the x-axis extending to the right and y-axisextending upward at ninety degrees to the x-axis. In this convention,when both ferrules are rotating through positive angles in their owncoordinate systems they are counter-rotating at the optical interfacebecause they face in opposite directions.

The radii of the tracks on which each of the output fibers rotates andthe angle between the line joining each fiber to the x-axis isdetermined by the following equations (with angle in degrees): ##EQU5##

    θ.sub.i =atan(y.sub.i /x.sub.i) if x.sub.i >0 and y.sub.i >0 (points are in the first quadrant)                                [13]

    θ.sub.i =atan(y.sub.i /x.sub.i)+180 if x.sub.i <0 and y.sub.i <0 (points are in the second quadrant)                       [14]

    θ.sub.i =atan(y.sub.i /x.sub.i)+180 if x.sub.i <0 and y.sub.i <0 (points are in the third quadrant)                        [15]

    θ.sub.i =atan(y.sub.i /x.sub.i)+360 if x.sub.i >0 and y.sub.i <0 (points are in the fourth quadrant)                       [16]

A further rotational transformation of the coordinates of the outputfibers is performed so that the multimode reference fiber or pen ispositioned on the positive x-axis. The x-y coordinates of all the outputsingle-mode fibers are calculated in this new reference frame. The sameprocedure is used for the input fibers in a N×N mechanical opticalswitch.

The next step 251 uses the estimated value of the ferrule offset tocalculate relative switch coordinates from the reference multimode port.FIG. 16 illustrates the alignment condition for an arbitrary inputfiber. The distance between the centers of the two ferrules is theV-groove offset d when the ferrules having the same outside diameters.Ferrules of unequal diameters may be used without departing from theteaching of the invention. Points 264 and 265 are respectively thecenter of the output ferrule and the center of the input ferrule. Point266 is the intersection point on the closed curves of the input fiberwith one of the output fibers. From the geometry of triangles, thefollowing equations are derived:

    r×sin (θ1)=R×sin (φ1)                [17]

    R×cos (φ1)=d-r×cos (θ1)              [18]

Solving equations 17 and 18: ##EQU6## Equations [19] and [20] give thealignment conditions for each fiber relative to the positive x-axis.Since each fiber's polar coordinates are known, the alignmentcoordinates for each fiber relative to the alignment coordinates of anyother fiber can be calculated. The relative switch coordinates arepassed to the measurement alignment station 230 where they are stored incomputer 234 and used as the starting values for peaking the alignmentof the input fibers or fiber with the output fibers.

As previously described, the fiber bundle 235 has the input and outputferrules 144 and 146 disposed at either end and contains the single-modefibers and the multimode reference fiber and is cut in half after thealignment station steps. The ferrules are secured in the mountingmembers of the mechanical optical switch 20 and connected to the drivemotors on the switch 20. The assembled switch is connected to themeasurement alignment station 230 in step 252 with a laser source 23 1coupled to the input single-mode fiber 235 as shown in FIG. 12. Thesingle-mode fiber bundle 236 and the reference fiber 237 arerespectively connected to the power meters 232 and 233. Power metercontrol cables 238 and 239 connect the power meters to the computer. Aswitch control cable 240 connects the optical switch to the computer.Step 252 further includes aligning the multimode reference port or fiberwith the input single mode fiber using a blind search routine as shownin FIG. 17.

The input and output ferrules 144 and 146 are assembled in mechanicaloptical switch 20 without respect to the location of the reference port262 and the input fiber to the home position sensors 52 of the switch20. On initial power-up of the mechanical optical switch 20, the drivemotors 46 coupled to each ferrule rotate to the home position defined bythe sensors 52. The blind search routine may be initialized at thispoint to a Home-Away-From-Home position, which is one hundred and eightydegrees from the home position, but to speed-up the search an operatormay manually control the motor rotation to position the inputsingle-mode fiber and the reference fiber in the same quadrant. Theblind search routine starts with both the input ferrule 144 and theoutput ferrule 144 at the arbitrary start position (ASP) or theHome-Away-From-Home (HAH) position, block 270. In the below descriptionof the blind search routine, the degrees of rotation at each step areillustrative and may be adjusted for some steps as experience dictates.In addition, the degrees of rotation will be a function of the number ofsingle-mode fibers in the output ferrule 146. Further, even though theroutines describe degrees of rotation, the actual data saved for theangular coordinates of the aligned fibers is in motor steps. The outputferrule is rotated through five to fifteen degree of rotation in block271 and the output optical power from the reference fiber is measuredand compared to a threshold in decision block 272. If the optical poweroutput does not exceed the threshold and the output ferrules has notexceeded 360 degrees of rotation from the ASP or HAH position as shownin decision block 273, then the routine loops back and rotates theoutput ferrule by another five to fifteen degrees of rotation, block271. If the output ferrule has exceeded the 360 degrees of rotations,then the output ferrule is reset to the ASP or HAH position and theinput ferrule is rotated by five to fifteen degrees of rotation as shownin block 274 and the output ferrules is again rotated by five to fifteendegrees, block 271. The input and output ferrules are rotated until theoutput power measured by the optical power meter exceeds the thresholdwhereupon a peaking routine is executed, block 275.

The peaking routine, shown in FIG. 18, starts by defining the inputferrule equal to one and clockwise rotation equal to one as shown inblocks 281 and 282. The current stepper motor coordinates are defined asthe best coordinates as shown in block 282. The assumption is that thereis some light coupled from the input fiber to the output fiber. Theroutine is initialized by defining the current stepper motor coordinatesas the last best coordinates and setting a variable N to zero as shownin block 284. The routine initializes the ferrule to minus one and therotation to minus one in block 285. That is, the output ferrule isrotated in a counter-clockwise direction on the first peaking pass. Theroutine starts with rotating the output ferrule in a counter-clockwisedirection to determine the coordinates having the maximum amount ofoptical power coupled from the input fiber to the output fiber. Thecoordinates are saved as the best coordinates. These steps are shown inblocks 286 through 289. The routine continues past the best coordinatesfor two more steps, block 290, and then starts to rotate the outputferrule in a clockwise direction by setting N equal to one and therotation equal to minus one, blocks 291 and 292. The routine determinesthe coordinates having the maximum amount of optical power coupled tothe output fiber for the clockwise rotation of the output ferrule andsaves the coordinates as the best coordinates, repeating blocks 286through 289. With n equal to one the routine goes to the bestcoordinates, block 293, and compares the best coordinates to the lastbest coordinates, block 294. If they are not the same for both motors,the routine loops back through the routine, blocks 283 and 284 toredefine the current stepper motor coordinates as the best coordinatesand the current stepper motor coordinates as the last best coordinatesand reset N equal one. What has changed in the coordinates is the outputferrule stepper motor coordinate. The routine then switches to the inputferrule by setting the ferrule to a positive one (-1 ×-1=1), block 285.The input ferrule is rotated in both the counter-clockwise and clockwisedirection to determine the best coordinate for the input ferrule,repeating blocks 286 through 292. After the best coordinate for theinput ferrule is determined the routine compares the best coordinates tothe last best coordinates, block 294, to determine if they are the samefor both motors. If the result is yes, the routine determines if bothmotors have cycled, block 295. If the results yes, the best coordinatesare saved as the optimum alignment positions for the input fiber and theselected output fiber, block 296. The routine then returns to the blindsearch routine or the routine that called it. The blind search routinethen returns to the alignment routine. The number of steps from the homeposition of each stepper motor to the alignment point is saved as thecoordinates of the intersection point.

The alignment routine proceeds to the coordinates for port number two,step 253, which is the first single-mode fiber, and uses the peakingroutine previously described, to determines the optimum coordinates formaximum light throughput from the input fiber to the output fiber. Theroutine recalculates the ferrule offset using the alignment data fromport two, step 254. Equation [19] gives θ1 as a function of r, d, and R.Although θ1 is not known, the change in θ1 is known as a function ofaligning port two using the peaking routine. The change in θ1 is thedifference between the calculated angular coordinate for port two andthe alignment coordinate found using the peaking routine. The assumptionis that the error is due to the estimate of the offset d, and as Suchthe derivative of equation [19] can be used to estimate a correctionfactor for the offset. Using the correction factor, the value of offsetd can be altered and new alignment coordinates can be recalculated forthe fibers. This procedure may be followed each time a new port isaligned, until the changes in alignment coordinate falls below somepreset threshold.

Taking the derivative of equation [15] with respect to d, rearranging,and replacing differentials with deltas: ##EQU7## The routines goes tothe calculated coordinates for port three, step 255, and aligns the portwith the input fiber using the peaking routine. The routine againrecalculates the ferrule offset using the port three alignmentcoordinates and recalculates the relative alignment coordinates for allthe other ports relative to port three, step 256. The routine goes tothe next port and each succeeding port and aligns the fibers using thepeaking routine, step 257. Each time a port is aligned the routinedetermines if it is the last port, step 258. When the last port has beenaligned, the routine stops, step 259. The stored best coordinates foreach of the aligned ports are read into memory circuits on the switchand stored. The switch 20 is now ready for use.

As has been previously described, the mechanical optical switch of thepresent invention may be configured with any number of input and outputfibers or ports. The basic operation of the switch is to rotate theinput or first optical fiber on its closed curve to one of the twointersecting points on its closed curve in response to the angularcoordinate representative of the position of the fiber at theintersecting point matching the intersecting point of the second opticalfiber. The output or second optical fiber is rotated on its closed curveto the intersecting point corresponding to the intersecting point of thefirst fiber in response to the angular coordinate representative of theposition of the second fiber at the intersecting point. These rotationalmovements may be performed sequentially, but in the preferred embodimentthey are performed simultaneously. Since the offset closed curvesintersect at two unique points, the speed of the switch may be increasedby selecting the intersecting points closest to the input and outputfibers prior to rotating the fibers.

Testing has shown that one ferrule can move the other when it rotates inthe same sense as the other, after the other ferrule has stoppedrotating. To overcome this problem each fiber is rotated past theselected intersecting point by the same amount and then both arecounter-rotated simultaneously and stopped at the same time at theintersecting point. Testing has also shown that one or both of the inputor output rotating sections of the switch can continue turning theirdrive lines until the fiber break or the motors stall. The switch hasbeen configured to generate an interrupt signal when either of themotors drive the drive line assemblies more than one or one and one/halftimes from their respective home positions. The reflectors or slottedwheels attached to the respective drive line assemblies pass light tothe respective detectors at the home position. A user error code isgenerated when this condition occurs and the motors stops.

An invalid fiber or port request can be issued to the switch. For thisreason, each input and output fiber or port selection is validated priorto rotating the input or output sections of the switch. Maximum limitsare set for the input and output sections based on the number of fiberin the respective sections. If the fiber or port request exceeds themaximum limits, a user error code is generated and the sections remainstationary.

In switch configurations where the input and output sections havemultiple fibers or ports, individual fibers are selected for either theinput or output sections prior to rotating the sections. It is possiblewhen selecting a new fiber or port for the maximum fiber or portposition to be exceeded. To prevent this condition from damaging theswitch, the angular coordinate to the intersecting point of a newlyselected fiber or port is summed with the angular coordinate of theintersecting point of the previously selected fiber or port. The summedangular coordinate value is compared to a maximum range value and a usererror code is generated when the summed angular coordinates exceed themaximum range value. The angular coordinates in the preferred embodimentare stored as steps of the stepper motor.

Referring to FIG. 19, there is shown a perspective view of an improvedmechanical fiber optical switch 300 according to the present invention.Switch 300 has a housing 302 having a base 303, end walls 304 and 306and sidewalls 308 and 310 forming a cavity 312. Disposed within thecavity 312 is a central pedestal 314 of similar design to the pedestal34 in FIG. 3. Holder assemblies having a similar design to the holderassemblies in FIGS. 7A and 7B are formed in the pedestal 314. The holderassemblies include offset V-grooves and spring clamps for holding themounting members 350. A recess 316 is formed in the top of the housing302 for receiving a gasket (not shown). The gasket is secured in therecess 316 by a top plate (not shown), which is similar to the top plate40 in FIG. 3. Like the switch 20 in FIG. 3 a circuit board (not shown)containing electronic circuitry is mounted on the switch housing 302.The cavity 314 is enclosed by the top plate and may be filled with anappropriate index matching fluid to reduce back refections of the inputlight passing between the input fibers 315 and output fibers 317.

Drive motors 318 and 320, such as stepper motors or DC motors withencoders, are secured to the sidewall 310 by motor clamps 322 and 324.Gear clamps 326 and 328 secure toothed spur gears 330 and 332 to thedrive motor 318 and 320 shafts. Bores 334 and 336 (bore 336 beingvisible) are formed in the respective end walls 304 and 306 forreceiving mounting member drive line assemblies 338 and 340. Mounted onthe base 303 are detector brackets 342 and 344 for mounting reflectivesensors 346 and 348, such as manufactured and sold by Honeywell, Inc.,Minneapolis, Minn., under part number HOA1160.

The housing 302, the top plate, motor clamps and detector brackets maybe made of the same material as the housing 22 in FIG. 3. In theimproved design these pans are milled or formed aluminum. The drivemotors 318 and 320 are stepper motors manufactured and sold by HSI, Inc.Waterbury, Conn., under part number 33755-01. The gear clamps 326 and328 used in the current design are manufactured and sold by W. M. Berg,Inc., East Rockaway, N.Y. under pan number CG1-25-A. The toothed spurgears are manufactured and sold by PIC Precision Industrial ComponentsCorp., Middlebury, Conn. under part number H47-72.

Referring to FIG. 20 there is shown a plan view of the opposing mountingmembers and one of the two similarly designed mounting member drivelines 338 and 340. The mounting member drive line has a mounting member350, such as a ferrule or the like, having one end coupled to a strainrelief coupling 352. The other end of the mounting member 350 has asleeve member 354 secured thereto, the purpose of which will bedescribed in greater detail below. Coupled to the other end of thestrain relief coupling 352 is a flexible drive shaft coupling 356, suchas a flexible bellows manufactured by Servometer Corp., Ceder Grove,N.J., under part number FC-1. For use in the mechanical fiber opticswitch of this design, the stock couplings of the bellows have beenreplaced and the interior bore has been enlarged. One end of theflexible drive shaft coupling 356 fits into the end of the strain reliefcoupling 352 and the other end fits over a drive shaft 358. The driveshaft is a stainless steel part, such as manufactured by PIC PrecisionIndustrial Components Corp., Middlebury, Conn. under part number A3-23or by W. M. Berg, Inc., East Rockaway, N.Y., under part number S4-23.Mounted on the drive shaft 358 is a retaining ring 360, such asmanufactured by W. M. Burg, Inc. under part number Q7-25. Mounted on thedrive shaft 358 next to the retaining ring 360 is an inner race spacer,such as manufactured by W. M. Berg, Inc., under part number SS2-32.Bearings 364 and 366, such as manufactured by W. M. Berg, Inc. underpart number B1-31-Q3, are mounted on the drive shaft 358 next to thespacer 362. Positioned between the bearings 364 and 366 is a beatingspacer 368, such as manufactured by W. M. Berg, Inc. under part numberSS2-65. Positioned on the drive shaft 358 adjacent to the bearing 366 isan outer race spacer 370, such as manufactured by W. M. Berg, Inc. underpart number SS3-13, which is followed by another retaining ring 372,such as manufactured by W. M. Berg, Inc. under part number Q4-50. A seal374, such as manufactured by Bal Seal Engineering Co., Inc., Santa Ana,Calif. under part number R315LB-202-SP-45, is positioned adjacent to theretaining ring 372. The end of the seal 374 opposite the retaining ring372 has a flange 376, which fits into a recess formed in the outersurface of the end walls 304 and 306 and surrounds the apertures 334 and336. A seal cover 378 and an outer race spacer 380 are positionedagainst the seal 374. The seal cover and the outer race spacer 380 haveco-extensive apertures formed therein for receiving screws or the like.The seal cover 378 and the outer race spacer 380 are secured to theouter surface of the end walls 304 and 306 with the screws for securingthe seal 374 in the housing 302. Positioned on the drive shaft 358adjacent to the outer race spacer 380 is a bearing 382, such asmanufactured by W. M. Berg, Inc. under part number B1-31-Q3, and anotherinner race spacer 384, such as manufactured by W. M. Berg, Inc. underpart number SS2-30. A toothed spur gear 386, similar to the gears 330and 332, are mounted on the drive shaft 358 and secured thereto by gearclamp 388, similar to gear clamps 326 and 328. A reflector code wheel390 is mounted on the end of the drive shaft 358 in line with one of thereflective sensors 346 or 348. The improved simplified drive line hasfewer coupling joints compared to the drive line in FIGS. 4 and 5.Further, all couplings are either bonded with an epoxy, such as TRA-BondBA-F230 epoxy or Epo-tek 353ND epoxy, or clamped in place with asplit-hub restraining device.

As previously described with regard to the mounting member ferrule 86,mounting member ferrule 350 may be formed of a borosilicate glass.Extensive testing of the mechanical fiber optic switch of the presentinvention has shown that the end-faces of the glass ferrules 350 werewearing against each other. This wear resulted in damaged fibers at theoptical interface. Sometimes the fibers also became contaminated by wearparticles. The problem exhibited itself as a gradual, but sometimeserratic, increase in switch insertion loss. The cross-sectional view ofFIG. 21 along line A--A' of FIG. 20 shows how the use of ceramic sleeves354 resolved this problem. The ceramic sleeves 354, such as manufacturedand sold by Mindurm Precision Products, Rancho Cucamonga, Calif., areepoxied to the end faces of the glass ferrules 350. The ferrule,populated with optical fibers, and the sleeves 354 are polished as amonolithic part. Since the ceramic is much harder than the glass, itpolishes more slowly. This results in an under-polish 392, with thesurface of the glass roughly 11-15 microns below the surface of theceramic. Consequently, the glass ferrules do not tough at all asrepresentatively shown in FIG. 21. The ceramic sleeves keep the ferrulesseparated by about 25 microns. Additionally, since the ceramic wearsmuch better than the glass, there are fewer wear particles to causeproblems with contamination. An alternative to using ceramic sleeveswith glass ferrules, is to replace the glass ferrules with ceramicferrules, such as manufactured and sold by Rikei of America, Cupentino,Calif. Less under polishing of the fibers will occur with the ceramicferrules but this may be advantageous in slightly reducing the insertionloss due to less longitudinal misalignment. A preferred material for usein forming the ceramic sleeves 354 and the ceramic ferrules is zirconiumoxide having a fracture toughness of 8 MPa*m 1/2.

Another problem discovered during the extensive testing of themechanical fiber optic switch of the present invention was that theferrules were differentially wearing into the V-grooves too fast,causing the switch to go out of alignment. This problem exhibited itselfas a gradual increase in insertion loss, punctuated occasionally bysharp changes in the insertion loss. A solution to this problem islining the V-grooves and the spring clamps with wear resistant ceramicinserts of zirconium oxide similar in composition to the ceramic sleeves364 and ferrules 350. Sapphire inserts, used with the glass ferrules,may also be a solution to this problem.

A further problem was encountered in bonding the wear resistant quartzinserts in the V-grooves. Hard and rigid bonding agents, such asepoxies, cause the inserts to warp. To prevent the epoxies from warpingthe inserts, the thickness of the inserts were increased to 0.062 inchesthick. This has greatly reduces the amount of warping.

A further embodiment of the mechanical optical switch 20 is to add aphotodiode within the switch 20 proximate to the interface between theinput and output fiber arrays 148 and 150. The photodiode monitors theamount of light scattered near the optical interface between the arrays148 and 150 and generates an electrical output as a function of themisalignment of the various ports of the switch 20. A minimum electricalsignal from the photodiode indicates the maximum alignment between theselected input and output ports. Including the photodiode in themechanical optical switch 20 permits active alignment of the ports afterit has been put in use. This can extend the useful life of the switch20.

Having aligned the ports of the switch 20, it is now usable in remotefiber test systems. It is envisioned that such systems are part of acentral office system of a telecommunications company as isrepresentatively shown in FIG. 22. The central office 400 has a centraloffice switch 402 coupled to optical fiber links 404, 406, and 408,which are connected to other central office switches 410, 412, and 414in remote central offices 416, 418, and 420. The optical fiber links404, 406, and 408 consist of optical transmission fibers for carryingoptical communications and an optical test fiber, also called a "darkfiber" in the industry. The optical switch 422 of the present inventionis tied into the central office switch 402 as part of a remote fibertest system. The test system includes at one measurement test instrument424, such as an optical time domain reflectometer (OTDR), an opticalpower meter, SDH/SONET test set, or the like coupled to the input portor fiber of the switch 422. The output fibers or ports of the switch 422are coupled to the optical fiber links 404, 406, and 408 via opticalcouplers 426, 428, and 430. Couplers 426, 428, and 430 may be wavelengthdivision multiplexers (WDM).

In one application, the WDMs 426, 428, and 430 are coupled to the "darkfibers" in the optical fiber links 404, 406, and 408 and the measurementtest instrument 424 is an OTDR. A central office computer passescommands to the switch 20 over a bus for connecting a particular inputport to a particular output port. The electronic circuitry on the switch20 interprets the command and accesses the stored coordinate positionsfor the selected ports and rotates each port to the intersection pointon the closed curves of the ports. Commands are sent to the opticalswitch 422 to align a particular output fiber or port with the inputfiber or port coupled to the OTDR 424. For example, output port 1 of theswitch 424 maybe coupled to the "dark fiber" of the optical fiber link404 through WDM 426. The OTDR 424 launches optical pulses into the "darkfiber" and the return reflected optical backscatter signal is coupled tothe OTDR 424 through the WDM 426 and the optical switch 422. The OTDR424 processes the return optical signal and produces a display or tableindicating the presence of anomalies in the fiber, such as reflections,losses, and the like. Additional commands can be sent to the opticalswitch 422 for aligning any of the other output fiber or ports to theinput fiber or port for examining the other "dark fibers" in the otheroptical links. Further, additional pieces of measurement test equipmentmay be coupled to additional input fibers or ports of the optical switch422.

The output fiber or ports of the optical switch can also be connected tothe optical transmission fibers of the optical links via WDMs connectedto these fibers. In examining active transmission fibers with an OTDR,the wavelength of the optical output of the OTDR 424 is different fromthe wavelength of the active optical transmissions over the transmissionfibers. For example; if the transmission link is operating at 1310 nmwavelength, then the OTDR 424 operates at 1550 nm wavelength forexamining the transmission fibers of the link. These tests can beperformed while active transmissions are occurring in the fiber.

Another application for the remote fiber test system is performingSDH/SONET performance test using an SDH/SONET test set. Such a test sethas a transmitting instrument at one end and a receiver instrument atthe other end. As an example, the input fiber or port of the opticalswitch 422 is coupled to the SDH/SONET transmission instrument, as wasthe OTDR, at the central office 400. Central office 416 has theSDH/SONET receiver instrument 432 coupled to the input fiber or port ofoptical switch 434. The output port of the optical switch is connectedto the optical link 404 via a WDM 436. Commands are sent to the opticalswitches 422 and 434 to align their input and output ports to couple theSDH/SONET transmission and receiver instruments together via one of theoptical transmission fibers in the optical link 404. Each opticaltransmission fiber of the optical link can be coupled to one of therespective output fibers or ports of the optical switches vie WDMs toallow SDH/SONET testing of all of the transmission fibers in the link.

The mechanical optical switch 20 of the present invention has beendescribed using electrical stepper motors 46 for rotating input andoutput ferrules 144 and 146 to align the optical fibers 152 in the inputand output optical fiber arrays 148 and 150 representing the input andoutput optical ports of the switch. It is also possible to practice thepresent invention using manual means for aligning the input and outputoptical ports. In such a switch, the stepper motors 46 and the toothedspur gears 48 are replaced with reduction gear assemblies. The reductiongear assemblies engage the ferrules drive shaft spur gears 72 on theferrule drive shafts 62. A knob is provided for manually rotating thegear assembly and hence the ferrules 144 and 146 in the switch 20.Detents can be provided with the gear assembly to indicate alignmentlocations of the input and output ports. Alternately, alignment may beachieved by monitoring the appropriate output port for a maximum opticalsignal.

A mechanical optical switch has been described that meets cycle-to-cyclerepeatability, long-term repeatability, and absolute misalignmentspecifications. The switch is inexpensive and easy to manufacture. Theswitch has offset ferrules that rotate about independent axes with theferrules being held independently in separate three-point kinematicallycorrect mounts, such as V-blocks. The V-blocks are lined with awear-resistant material, such as glass or ceramic and lubricated with anindex matching fluid. Offsetting the ferrules and mounting then inkinematically correct mounts allows the fibers held within the ferrulesto trace out closed curves with the closed curves of the fibers in theinput ferrule intersecting the closed curves of the fibers in the outputferrules. The input ferrule and the output ferrule are fully filled withfibers with all the fibers being accessible as ports with the exceptionof the fibers centered on the axes of the ferrules. Additionally, theceramic sleeves are used to reduce the insertion loss between the inputand output fibers over time by reducing the wear at the opticalinterface. Further, the optical switch is useable in a remote fiber testsystem for performing test on optical fiber links using opticalmeasurement test equipment. These and other aspects of the presentinvention are set forth in the appended claims.

What is claimed is:
 1. An alignment apparatus for determining angularcoordinates of intersecting points of offset closed curves in an opticalswitch having at least a first optical fiber disposed within a firstmounting member rotating about a first independent and offset rotationalaxis with the first optical fiber positioned within the mounting memberto move on a first closed curve and a plurality of optical fibersdisposed within a second mounting member with the plurality of opticalfibers within the second mounting member rotating about a secondindependent and offset rotational axis with the plurality of opticalfibers positioned within the second mounting member to move on closedcurves, the first and second mounting members having end faces inopposing relationship forming an optical interface between the firstoptical fiber and the plurality of optical fibers, with the first andsecond rotational axes being laterally offset from each other foroffsetting the first closed curve from the closed curves of theplurality of optical fibers for the establishing intersecting pointsbetween the closed curves of the plurality of optical fibers within thesecond mounting member and the closed curve of the first optical fibercomprising:an analytical apparatus for imaging the respective end facesof the first and second mounting members for determining the respectiveaxes of rotation of the mounting members, the locations of the opticalfibers in the respective mounting members and coordinates of the opticalfibers relative to the axis of rotation of the respective mountingmembers, the location of at least one reference point within one of themounting members, and relative angular coordinates of intersectingpoints between each of the closed curves of the plurality of opticalfibers within the second mounting member and the closed curve of thefirst optical fiber as a function of the offset of the first and secondmounting members and the reference point; and a measurement alignmentapparatus receiving the relative angular coordinates of the intersectingpoints between each of the closed curves of the plurality of opticalfibers within the second mounting member and the closed curve of thefirst optical fiber from the analytical apparatus for determining theangular coordinates of the intersecting points between each of theplurality of optical fibers and the first optical fiber as a function ofoptimally aligning the first optical fiber with each of the plurality ofoptical fibers.
 2. The alignment apparatus as recited in claim 1 whereinthe analytical apparatus further comprises a microscope having a stageon which is mounted a holder assembly for receiving the first and secondmounting members.
 3. The alignment apparatus as recited in claim 1wherein the analytical apparatus further comprises a light source forcoupling light into the first optical fiber and the plurality of opticalfibers.
 4. The alignment apparatus as recited in claim 2 wherein theanalytical apparatus further comprises a camera coupled to themicroscope for generating images of the end faces of the first andsecond mounting members respectively containing the first optical fiberand the plurality of optical fibers.
 5. The alignment apparatus asrecited in claim 4 wherein the camera is a video camera for generatingvideo images.
 6. The alignment apparatus as recited in claim 5 whereinthe video camera is a charged coupled device camera.
 7. The alignmentapparatus as recited in claim 5 wherein the analytical apparatus furthercomprises a video monitor coupled to the video camera for generatingvisual presentations of the end faces of the first and second mountingmembers respectively containing the first optical fiber and theplurality of optical fibers.
 8. The alignment apparatus as recited inclaim 7 wherein the analytical apparatus further comprises a framegrabber for acquiring images of the end faces of the first and secondmounting members respectively containing the first optical fiber and theplurality of optical fibers from the video monitor and generatingdigital values representative of the acquired images.
 9. The alignmentapparatus as recited in claim 8 wherein the analytical apparatus furthercomprises a computing means for receiving the digital valuesrepresentative of the acquired images of the end faces of the first andsecond mounting members respectively containing the first optical fiberand the plurality of optical fibers and determining under programcontrol the respective axes of rotation of the mounting members, thelocations of the optical fibers in the respective mounting members andthe coordinates of the optical fibers relative to the axis of rotationof the respective mounting members, the reference point within one ofthe mounting members, and the relative angular coordinates ofintersecting points between each of the closed curves of the pluralityof optical fibers within the second mounting member and the closed curveof the first optical fiber as a function of the offset of the first andsecond mounting members and the reference point.
 10. The alignmentapparatus as recited in claim 1 wherein the measurement alignmentapparatus further comprises a laser light source coupled to the firstoptical fiber.
 11. The alignment apparatus as recited in claim 10wherein the measurement alignment apparatus further comprises first andsecond optical power meters coupled to the plurality of optical fiberswith the first optical power meter coupled to a multimode referencefiber acting as the reference point in the second mounting member andthe second optical power meter coupled to the remaining plurality ofoptical fibers.
 12. The alignment apparatus as recited in claim 11wherein the measurement alignment apparatus further comprises acomputing means coupled to the first and second optical power meters andthe optical switch for determining under program control the angularcoordinates of the intersecting points between each of the plurality ofoptical fibers and the first optical fiber as a function of optimallyaligning the first optical fiber with each of the plurality of opticalfibers.